CA1262360A - Process for separating isomers of toluenediamine - Google Patents
Process for separating isomers of toluenediamineInfo
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- CA1262360A CA1262360A CA000525887A CA525887A CA1262360A CA 1262360 A CA1262360 A CA 1262360A CA 000525887 A CA000525887 A CA 000525887A CA 525887 A CA525887 A CA 525887A CA 1262360 A CA1262360 A CA 1262360A
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- adsorbent
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- toluenediamine
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C211/00—Compounds containing amino groups bound to a carbon skeleton
- C07C211/01—Compounds containing amino groups bound to a carbon skeleton having amino groups bound to acyclic carbon atoms
- C07C211/26—Compounds containing amino groups bound to a carbon skeleton having amino groups bound to acyclic carbon atoms of an unsaturated carbon skeleton containing at least one six-membered aromatic ring
- C07C211/27—Compounds containing amino groups bound to a carbon skeleton having amino groups bound to acyclic carbon atoms of an unsaturated carbon skeleton containing at least one six-membered aromatic ring having amino groups linked to the six-membered aromatic ring by saturated carbon chains
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
- C07C209/82—Purification; Separation; Stabilisation; Use of additives
- C07C209/86—Separation
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- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Solid-Sorbent Or Filter-Aiding Compositions (AREA)
Abstract
"PROCESS FOR SEPARATING ISOMERS OF TOLUENEDIAMINE"
ABSTRACT OF THE DISCLOSURE
This invention comprises a process for separating 2,4 toluenediamine from a feed mixture comprising 2,4-toluene-diamine and 2,6-toluenediamine, which process comprises contacting the mixture at adsorption conditions with an adsorbent comprising a Y type zeolite cation-exchanged with Ni or Ca or an X type zeolite cation-exchanged with Ca, Ba, Na, Ni and K, or an L type zeolite cation-exchanged with a K
cation, thereby selectively adsorbing one of isomers of toluenediamine. The remainder of the feed mixture is removed from the adsorbent and the adsorbed toluenediamine isomer is recovered by desorption at desorption conditions with a desorbent material comprising a lower alcohol or an amine..
ABSTRACT OF THE DISCLOSURE
This invention comprises a process for separating 2,4 toluenediamine from a feed mixture comprising 2,4-toluene-diamine and 2,6-toluenediamine, which process comprises contacting the mixture at adsorption conditions with an adsorbent comprising a Y type zeolite cation-exchanged with Ni or Ca or an X type zeolite cation-exchanged with Ca, Ba, Na, Ni and K, or an L type zeolite cation-exchanged with a K
cation, thereby selectively adsorbing one of isomers of toluenediamine. The remainder of the feed mixture is removed from the adsorbent and the adsorbed toluenediamine isomer is recovered by desorption at desorption conditions with a desorbent material comprising a lower alcohol or an amine..
Description
3g~
"PROCESS FOR SEPARATING ISOMERS OF TOLUENEDIAMINE"
FIELD OF THE INVENTION
The field of art to wnich this invention pertains is the solid bed adsorptive separation of isomers of toluenediamines (TDA). More specifically, the invention relates to a process for separating 2,4-toluenediamine from
"PROCESS FOR SEPARATING ISOMERS OF TOLUENEDIAMINE"
FIELD OF THE INVENTION
The field of art to wnich this invention pertains is the solid bed adsorptive separation of isomers of toluenediamines (TDA). More specifically, the invention relates to a process for separating 2,4-toluenediamine from
2,6-toluene diamine and other toluenediamine isomers by employing a solid bed adsorption system.
BACKGROUND OF THE INVENTION
The isomers, 2,4-toluenediamine and 2,6-toluenediamine are important precursers of polyurethanes which are useful in many applications as rigid or flexible forms or as fibers, e.g., insulation, soundproofing, interlinings for clothing and sleeping bags, cushions, spandex, etc.
It is common industrial practice to make polyurethane from a mixture of the isomers, 2,4- and 2,6-toluene diisocyanate (TDI), for example 80/20 or 65/35, derived from mixtures of 2,4- and 2,6-toluenediamine, because it is difficult and expensive to separate them by existing techniques. Current methods of separating the isomers involve crystallization, e.g. U.S. Patent No. 4,246,187, and hence, are energy-intensive and time-consuming. Moreover, polyurethanes derived from pure 2,4-toluenediamine have dramatically different properties compared to materials synthesized from mixtures. It is further expected that polyurethanes synthesi~ed from (relatively3 pure 2,6-toluenediamine ~ill have different and more useful properties, for example, a higher glass transition temperature, Tg, a-nd greater stability. Also, the reaction speed with a single isomer is expected to be more consistent. Accordingly, it is desirable to separate the TDI isomers or their precursors, the toluenediamines, by an economical process.
It is well known in the separation art that certain crystalline aluminosilicates can be used to separate hydrocarbon types from mixtures thereof. Furthermore, X and Y zeolites have been employed in a number of processes to separate individual hydrocarbon isomers.
It is known from U.S. Patent No. 3,069,470 to Fleck et al, to use type X zeolites for the separation of the meta isomer from other isomers of toluidine. In U.S. Patent No.
4,4~0,129 to Priegnitz et al, it is disclosed to separate p-toluidine from its isomers with an X- or Y- type zeolite exchanged with Fe, Mn, Co, Ni or Zn and a desorbent comprising aniline or, when using an X-type zeolite, alkylamine having greater than eight carbons.
It is known from U.S. Patent No. 4,270,013 to Priegnitz et al that ortho-nitrotoluene may be separated From other nitrotoluene isomers by using a type X zeolite containing at exchangeable cationic sites one cation selected from a group that includes potassium and barium. The specific desorbent materials disclosed by this reference are toluene and 1-hexanol. The separation of isomers of disubstituted benzenes with crystalline aluminosilicates having silica/alumina mole ratio oF at least l2 is disclosed in U.S. Patent No. 4,~67,126 to Zinnen.
The adsorptive separation of another precursor of polyurethane, 2,4-dinitro toluene and 2,6-dinitrotoluene has been disclosed and the separation is achieved by an L, X or Y type zeolite cation exchanged with K, Na, Ca, Ba, Li or Mg and desorbed by a C3 to C5 alcohol, a ketone, ester or a nitrocompound.
The separation of minor isomers9 2,3- and 3~4-dinitrotoluene, from the major isomers, ~94- and ?,6-dinitrotoluene, with a calcium or sodium exchanged Y type zeolite hass been disclosed. The desorbent can be an ester, an alcohol or a ketone. Presence of the minor isomers lowers the yield of polyurethane precursors and produces high molecular weight side products.
Alternatively, the final precursor of polyurethane, toluene diisocyanate, is normally available as mixtures of isomers. It is known that the separation of 2,4- and 2,6-diisocyanate (TDI) can be performed by adsorption onto a type Y zeolite exchanged with K, Ca, Na, Li, H, and Mg and desorbed with toluene. It is hypothesized that polyurethanes made with a single, pure isomer of TnI may exhibit improved properties.
SUMMARY OF THE INVENTI_ In brief summary, the invention is, in one embodiment, a process for separating 2,4-toluenediamine from a mixture comprising 2,4-toluenediamine and at least one isomer thereof, such as 2,6-toluenediamine. The process comprises contacting ~he mixture at adsorption conditions with an adsorbent comprising an X type zeolite cation exchanged with a cation from the group Ca, Na, K, Ni or a Y- type zeolite exchanged with a cation from the group Ca or Ni cations, thereby selectively adsorbing the 2,4-toluenediamine thereon. The remainder of the feed mixture is then removed from the adsorbent and the 2,4-toluenediamine recovered by desorption at desorption conditions with a desorbent material comprising a lower alcohol or an amine. In the process using an X-type of zeolite cation, exchanged with a barium cation or an L-type zeolite exchanged with a K
cation, the zeolite is 2,6-toluenediamine selective and hence 2,6-toluenediamine will be adsorbed by the zeolite.
It is advantageous to use a 2,6-toluenediamine - selective zeolite with commercially available feed mixtures of toluenediamine isomers which are 80~ 2,4-toluenediamine and 20~ 2,6-toluenediamine because extraction of the minor 2,6-component results in a more efficient and economical separation. Effective desorbents for this separation , whether 2,4- selective or 2,6- selective, have been found to comprise lower alcohols, e.y. methanol and ethanol and n-alkyl amines.
Other embodiments of our invention encompass details about feed mixtures, adsorbents, desorbent materials and operating conditions, all of which are hereinafter disclosed in the following discussion of each of the facets of the present invention.
BRI~F DESCRIPTION OF THE DRAWING
Figures 1-5 are chromatographic traces representing the separation of the isomers of toluenediamine by the pulse test method using different zeolite adsorbents and desorbents as generated in Examples 2-6.
DESCRIPTION OF THE INVENTION
At the onset, the definitions of various terms used throughout the specification will be useful in making clear the operation, objects and advantages of our process.
A "feed mixture" is a mixture containing one or more e~tract components and one or more raffinate components to be separated by our process. The term "feed stream"
indicates a stream of a feed mixture which passes to the adsorbent used in the process.
An "extract component" is a compound or type of compound that is more selectively adsorbed by th~ adsorbent while a "raffinate component" is a compound or type of compound that is less selectively adsorbed. In this process, 2,4- toluenediamine is an extract component and 296- toluenediamine is a raffinate component, when the adsorbent used is Ca X, Na X, ~i X, K X, Ca Y or Ni Y.
However, when the adsorbent used is Ba X or K L, 2,h-toluenediamine is an extract component and 294-toluene-diamine is a raffinate component. The term "desorbent material" shall mean generally a material capable of desorbing an extract component. The term "desorbent stream"
or "desorbent input stream" indicates the stream through which desorbent material passes to the adsorbent. The term "raffinate stream" or "raffinate output stream" means a stream through which a raffinate component is removed from the adsorbent. The composition of the raffinate stream can vary from essentially 100~ desorbent material to essentially 100% raffinate components. The "extract stream" or "extract output stream" shall mean a stream through which an extract material which has been desorbed by a desorbent material is removed from the adsorbent. The composition of the extract stream, likewise, can vary from essentially 100% desorbent material to essentially 100% extract components. At least a portion of the extract stream and preferably at least a portion of the raffinate stream from the separation process are passed to separation means, typically fractionators, where at least a portion of the desorbent material is separated to produce an extract product and a raffinate product. The terms "extract product" and "raffinate product" mean products produced by the process containing, respectively, an extrac~ component and a raffinate component in higher concentrations than those found in the extract stream and the raffinate stream. Although it is possible by the process of this invention to produce a high purity product at high recoveries, it will be appreciated that an extract component is never completely adsorbed by the adsorbent, nor is a raffinate component completely nonadsorbed by the adsorbent. Therefore, varying amounts of a raffinate component can appear in the extract stream and, likewise, varying amounts of an extract component can appear in the raffinate stream. The extract and raffinate streams then are further distinguished from each other and from the feed mixture by the ratio of the concentrations of an extract component and a raffinate component appearing in the particular stream. More specifically, the ratio of the concentration of 2,4-toluenediamine (extract) to that of a less selectively adsorbed isomer, 2,6-toluenediamine (raffinate) will be lowest in the raffinate stream, next highest in the feed mixture, and the highest in the extract stream. Likewise, the ratio of the concentration of less selectively adsorbed 2,6-toluenediamine to that of more selectively adsorbed 2,~-toluenediamine will be highest in the raffinate stream, next highest in the feed mixture, and the lowest in the extract stream. In the embodiment where 2,6-toluenediamine is the selectively adsorbed compsnent~
the above ratios are reversed.
The term "selective pore volume" of the adsorbent is defined as the volume of the adsorbent which se1ectively adsorbs an extract component from the feed mixture. The term "non-selective void volume" of the adsorbent is the volume of the adsorbent which does not selectively retain an extract component from the feed mixture. This volume includes the cavities of the adsorbent which contain no adsorptive sites and the interstitial void spaces between adsorbent particles. The selective pore volume and non~
selective void volume are generally expressed in volumetric quantities and are of importance in determining the proper flow rates of fluid required to be passed into an operational zone for efficient operations to take place for a given quantity of adsorbent. When adsorbent "passes" into the operational zone employed in one embodiment of this process, its non-selective void volume together with its selective pore volume carries fluid into that zone. The non-selective void volume is utilized in determining the amount of fluid which should pass into the same zone in a countercurrent direction to the adsorbent to displace the fluid present in the non-selective void volume. If the fluid flow rate passing into a zone is smaller than the non-selective void volume rate of adsorbent material passing into that zone~ there is a net entrainment of liquid into the zone by the adsorbent. Since this net entrainment is a fluid present in the non-selective void volume of the ~ 3~ ~
adsorbent, it in most instances comprises less selectively retained feed components. The selective pore volume of an adsorbent can in certain instances adsorb portions of raffinate material from the fluid surrounding the adsorbent since in certain instances there is competition between extract material and raffinate material for adsorptive sites within the selective pore volume. If a large quantity of raffinate material with respect to extract material surrounds the adsorbent, raffinate material can be competitive enough to be adsorbed by the adsorbent.
The prior art has recognized that certain characteristics of adsorbents are highly desirable, if not absolutely necessary, to the successful operation of a selective adsorption process. Such characteristics are equally important to this process. Among such characteristics are: adsorptive capacity for some volume of an extract component per volume of adsorbent, the selective adsorption of an extract component with respect to a raffinate component and the desorbent material; and sufficiently fast rates of adsorption and desorption of an extract component to and from the adsorbent. Capacity of the adsorbent for adsorbing a specific volume of an extract component is, of course, a necessity; without such capacity the adsorbent is useless for adsorptive separation.
Furthermore, the higher the adsorbent's capacity for an extract component the better is the adsorbent. Increased capacity of a particular adsorbent makes it possible to reduce the amount of adsorbent needed to separate an extract component of known concentration contained in a particular charge rate of feed mixture. A reduction in the amount of adsorbent required for a specific adsorptive separation reduces the cost of a separation process. It is important that the good initial capacity of the adsorbent be maintained during actual use in the separation process over some economically desirable life.
The second necessary adsorbent characteristic is the ability of the adsorbent to separate components of the ~eed;
or, in other words, that the adsorbent possess adsorptive se1ectivity for one component as compared to another component. Relative selectivity can be expressed not only for one ~eed component as compared to another but can also be expressed between any feed mixture component and the desorbent material. The selectivity, (B), is defined as the ratio of the two components of the adsorbed phase divided by the ratio of the same two components in the unadsorbed phase at equilibrium condition, as shown in Equation 19 below:
Selectivity = (B) = ~vol. percent C/vol. percent D~A
~vol. percent C/vol. percent D~U
where C and D are two components of the feed represented in volume percent and the subscripts A and U represent the adsorbed and unadsorbed phases respectively. The equilibrium conditions were determined when the feed passing over a bed of adsorbent did not change composition after contacting the bed of adsorbent. In other words, there was no net transfer of material occurring between the unadsorbed and adsorbed phases. Where selectivity of two components approaches 1.0, there is no preferential adsorption of one component by the adsorbent with respect to the other; they are both adsorbed (or non-adsorbed) to about the same degree with respect to each other. As the (B) becomes less than or greater than 1.0, there is a pre~erential adsorption by the adsorbent for one component with respect to the other. When comparing the selectivity by the adsorbent of one component C over component D, a (B) larger than 1.0 indicates preferential adsorption of component C within the adsorbent.
A (B) less than 1.0 would indicate that component D is preferentially adsorbed leaving an unadsorbed phase richer in component C and an adsorbed phase richer in component D.
~ ~ 2 3~ ~
The third important characteristic is the rate of exchange of the extract component of the feed mixture material or, in other words, the relative rate of desorption of khe extract component. This characteristic relates directly to the amount of desorbent material that must be employed in the process to recover the extract component from the adsorbent, faster rates of exchange reduce the amount of desorbent mat~rial needed to remove the extract component and therefore permit a reduction in the operating cost of the process. With faster rates of exchange, less desorbent material has to be pumped through thP process and separated from the extract stream for reuse in the process.
Adsorbents to be used in the process of this invention will comprise specific crystalline aluminosilicates.
Particular crystalline aluminosilicates encompassed by the present invention include crystalline aluminosilicate cage structures in which the alumina and silica tetrahedra are intimately connected in an open three dimensional network to form cage-like structures with window-like pores of about 8 A free diameter. The tetrahedra are crosslinked by the sharing of oxygen atoms with spaces between the tetrahedra occupied by water molecules prior to partial or total dehydration of this zeolite. The dehydration of the zeolite results in crystals interlaced with cells having molecular dimensions and thus the crystalline aluminosilicates are often referred to as "molecular sieves", particuarly when the separation which they effect is dependent essentially upon differences between the sizes of the feed molecules as, for instance, when smaller normal paraffin molecules are separated from larger isoparaffin molecules by using a particular molecular sieve.
In hydrated form, the crystalline aluminosilicates used in the process of this invention generally encompass those zeolites represented by the Formula 1 below:
~ ~ 23 Formula I
M2/no:Al2o3:wsio2 y~2o where "M" is a cation which balances the electrovalence of the aluminum-centered tetranedra and wh;ch is generally referred to 35 an exchangeable cationic site, "n" represents the valence of the cation, "w" represents the moles of SiO2, and "y" represents the moles of water. The generalized cation "M" may be monovalent, divalent or trivalent or mixtures thereof.
The prior art has generally recogn;zed that adsorbents comprising L, X and Y zeolites can be used in certain adsorptive separation processes. These zeolites are described and defined in U.S. Patent Nos. 3,216,789, 2,882,244 and 3,130,007, respectively.
The X zeolite in the hydrated or partially hydrated form can be represented in terms of mole oxides as shown in Formula 2 below:
Formu1a 2 (o.9~o.2)M2~no:Al2o3:(2.5+o.5)sio2 yH2o where "M" represents at least one cation having a valence of not more than 3, "n" represents the valence of "M" and "y"
is a value up to about 9 depending upon the identity of "M"
and the degree of hydration of the crystal. As noted from Formula 29 the SiO2/A1203 mole ratio of X zeolite ls 2.5+0.5. The cation "M" may be one or more of a number of cations such as a hydrogen cation, an alkal~ metal catlon, or an alkaline earth cation, or other selected cations~ and is generally referred to as an exchangeable cationic site.
As the X zeollte is initially prepared, the cation "M" is usually predomlnately sodium, that ls, the major cation at the exchangeable cationic sites is sodium and the zeolite is therefore referred to as a sodium-X zeolite. Depending upon ~:'."', the purity of the reactants used to make the zeolite, other cations mentioned above may be present, however, as impurities. The Y zeolite in the hydrated or partially hydrated form can be similarly represented in the terms of mole oxides as in Formula 3 below:
Formula 3 (o~9+o~2)M2/no:Al2o3:wsio2 yH2o where "M" is at least one cation having a valence not more than 3, "n" represents the valance of "M", "w" is a value greater than about 3 up to about 6, and "y" is a value up to about 9 depending upon the identity of "M" and the degree of hydration of the crystal. The SiO2/Al203 mole ratio for Y
zeolites can thus be from about 3 to about 6. Like the X
zeolite, the cation "M" may be one or more of a variety of cations but, as the Y zeolite is initially prepared, the cation "M" is also usually predominately sodium. A Y
zeolite containing predominately sodium cations at the exchangeable cationic sites is therefore referred to as a sodium-Y zeolite or Na-Y zeolite.
The L zeolite in the hydrated or partially hydrated form may be represented in terms of mole oxides as in Formula 4 below:
Formula 4 o.g 1.3M2/no:Al2o3:5-2-6 9SiO2 y 2 where M designates at least one exchangeable cation as referred to above, n is the valence of M and y may be any value from O to about 9. It is preferred to synthesize the potassium form of the L-type zeolite since the reactants to make this form are readily available and generally water soluble. Thus the as-made form of the L-zeolite is referred to as potassium-L, or K-L, zeolite. L-zeolite is characterized by planar 12-ring pores aligned to produce ~ 3~ ~
one-dimensional channels, linked to each other by small pore openings which will not admit water molecules. A minor two-dimensional pore system also exists, parallel to the aforesaid channels.
Cations occupying exchangeable cationic sites in the zeolite may be replaced with other cations by ion exchange methods well-known to those having ordinary skill in the field of crystalline aluminosilicates. Such methods are generally performed by contacting the zeolite or an adsorbent mater~al containing the zeolite with an aqueous solution of the soluble salt of the cation or cations desired to be placed upon the zeolite. After the desired degree of exchange takes place, the sieves are removed from the aqueous solution, washed, and dried to a desired water content. By such methods the sodium cations and any non-sodium cations which might be occupying exchangeable sites as impurities in a sodium-X or sodium-Y zeolite can be par~ially or essentially completely replaced with other cations. The zeolite used in the process of this invention contains cations at exchangeable cationic sites selected from the group of metals K, Na, Ca, Ba,Co or Ni. The preferred zeolites are Ba X and K L~ which are selective for the minor isomer, 2,6-toluenediamine.
Typically, adsorbents used in separative processes contain zeolite crystals dispersed in an amorphous material or inorganic matrix. The zeolite will typically be present in the adsorbent in amounts ranging from about 75 to about 98 wt. % based on volatile-free composition. Volatile-free compositions are generally determined after the adsorbent has been calcined at 900C in order to drive off all volatile matter. The remainder of the adsorbent will generally be the inorganic matrix material such as silica, titania, or alumina or mixtures thereof, or compounds, such as clays, which material is present in intimate mixture with the small particles of the zeolite material. This matrix material may be an adjunct of the manufacturing process for ~ 3~ ~
zeolite (for example, intentionally 1ncomplete purification of elther zeolite during its manu~acture) or it may be added to relatively pure zeolite, but ln either case its usual purpose is as a binder to aid in forming or agglomerating the hard crystalline particles of the zeolite. Normally, the adsorbent will be in the form of particles such as extrudates, aggregates9 tablets, macrospheres or granules having a desired particle size range. The typical adsorbent will have a particle size range of about 16-6~ mesh (Standard U.S. Mesh). Examples of zeolites used in adsorbents known to the art, e~ther as is or after cation exchange, are "Molecular S;eves 13Xi' and SK-40" both of which are available from the Linde Company, Tonawanda, New York. The first material contains X zeolite wh;le the latter material contains Y zeolite.
Ideally, desorbent materials should have a selectivity equal to about 1 or slightly less than 1 with respect to all extract components so that all of the extract components can be desorbed as a class with reasonable flow rates of desorbent material and so that extract components can displace desorbent material in a subsequent adsorption step.
While separation of an extract component from a raf~lnate component is theoretically possible when the selectivity oF
the adsorbent for the extract component with respect to the raffinate component is ~ust slightly greater than 1.09 it is preferred that such selectivity be reasonably greater than 1Ø Like relative volatility, the hiyher the selectivity, the easier the separation is to perform. Higher selectivities permit a smaller amount of adsorbent to be used.
Desorbent materials used in various prior art adsorptive separation processes vary depending upon such factors as the type of operation employed. In the swing bed system in which the selectively adsorbed feed component is removed from the adsorbent by a purge stream desorbent~
selection is not as cr;tical and desorbent materials * Trade Mark ,~ ~
comprising gaseous hydrocarbons such as methane, ethane, etc., or other types of gases such as nitrogen or hydrogen may be used at elevated temperatures or reduced pressures or both to effectively purge the adsorbed feed component from the adsorbent. However, in adsorptive separation processes which are generally operated continuously at substantially constant pressures and temperatures to insure liquid phase, the desorbent material must be judiciously selected to satisfy many criteria. First, the desorbent material should displace an extract component from the adsorbent with reasonable mass flow rates without itself being so strongly adsorbed as to unduly prevent an extract component from displacing the desorbent material in a following adsorption cycle. Expressed in terms of the selectivity (hereafter discussed in more detail)9 it is preferred that the adsorbent be more selective for all of the extract components with respect to a raffinate component than it is for the desorbent material with respect to a raffinate component. Secondly, desorbent materials must be compatible with the particular adsorbent and the particular feed mixture. More specifically, they must not reduce or destroy the critical selectivity of the adsorbent for an extract component with respect to a raffinate component. Desorbent materials should additionally be substances which are easily separable from the feed mixture that is passed into the process. Both the raffinate stream and the extract stream are removed fro~ the adsorbent in admixture with desorbent material and without a method of separating at least a portion of the desorbent material, the purity of the extract product and the raffinate product would not be very high nor would the desorbent material be available for reuse in the process. It is therefore contemplated that any desorbent material used in this process will preferably have a substantially different average boiling point than that of the feed mixture to allow separa~ion of at least a portion of desorbent material from feed components in the extract and raffinate streams by simple fractional distillation, thereby permitting reuse of desorbent material in the process. The term "substantially different" as used herein shall mean that the difference between the average boiling points between the desorbent material and the feed mixture shall be at least about 5C. The boiling range of the desorbent material may be higher or lower than that of the feed mixture. Finally, desorbent materials should also be materials which are readily available and therefore reasonable in cost. In the preferred isothermal, isobaric, liquid-phase operation of the process of our invention, we have found that desorbent material comprising a lower alcohol, e.g. 9 methanol, ethanol, propanol or amines, e.g.
n-alkylamines, etc. will result in selectivity for the 2,4-toluenediamine isomer when used with an adsorbent selected from the group comprising Ca X, Na X, K X, Ni X, Ca Y or Ni Y and will result in selectivity for the 2,6- isomer when the absorbent is selected from the group Ba X or K L.
Methanol is the most preferred desorbent in this process.
Toluene, which acts as a diluent for the desorbent, can be used with any desorbent in amounts up to about 50 vol.%.
Certain combinations of adsorbent and desorbent were found to be most effective in separating the TDA isomers and therefore 9 the most preferred adsorbent-desorbent combinations are K-L zeolite with methanol desorbent, Na X
zeolite with ethanol and Ba X zenlite with methanol desorbent. Each of these combinations exhibited, in the pulse tests, good selectivity and resolution and well-shaped elution profiles. Furthermore, these desorbents are inexpensive, available chemicals, having low boiling points with respect to the TDA isomers.
The adsorbent may be employed in the form of a dense compact fixed bed which is alternatively contacted with the feed mixture and desorbent materials. In the simplest embodiment of the invention, ~he ~dsorbent is employed in the form of a single static bed in which case the process is only semi-continuous. In another embodiment, a set of two or more static beds may be employed in fixed bed contacting with appropriate valving so that the feed mixture is passed through one or more adsorbent beds while the desorbent materials can be passed through one or more of the other beds in the set. The flow of feed mixture and desorbent materials may be either up or down through the desorbent.
Any of the conventional apparatus employed in static bed fluid-solid contacting may be used.
Moving bed or simulated moving bed flow systems, however, have a much greater separat~on efficiency than fixed bed systems and are therefore preferred. In the moving bed or simulated moving bed processes 9 the retention and displacement operations are continuously taking place wh;ch allows both continuous production of an extract and a raffinate stream and the continuous use of feed and displacement fluid streams. One preferred embodiment of this process utilizes what is known in the art as the simulated moving bed countercurrent flow system. The operating principles and sequence of such a flow system are described in U.S. Patent No. 2,985,589.
In such a system, it is the progressive movement of multiple liquid access points down a molecular sieve chamber that simulates the upward movement of molecular sieve contained in the chamber. Reference can also be made to D.B. Broughton's U.S. Patent No. 2,985,589 and to a paper entitled, "Continuous Adsorptive Processing -A New Separation Technique" by D.B. Broughton presented at the 34th Annual Meeting of the Society of Chemical Engineers at Tokyo, Japan on April 2, 1969, for further explanation of the simulated moving bed countercurrent process flow scheme.
Another embodiment of a simulated moving bed flow system suitable for use in the process of the present invention is the co-current high efficiency simulated moving ~ .
~ 3~ ~
bed process disclosed in our assignee's U.S. Patent No.
4,402,~32.
It is contemplated with any flow scheme used to carry out the present invention that at least a portion of the extract output stream will pass into a separation means wherein at least a portion of the desorbent material can be separated to produce an extract product containing a reduced concentration of desorbent material. Preferably, but not necessary to the operatlon of the process, at least a portion of the raffinate output stream will also be passed to a separation means wherein at least a portion of the des~rbent material can be separated to produce a desorbent material stream which can be reused in the process and a raffinate product containing a reduced concentration of desorbent material. The separation means will typically be a fractionation column, the design and operation of wh~ch is well-known to the separation art.
Although both liquid and vapor phase operations can be used in many adsorptive separation processes, liquid-phase operat10n is preferred for this process because of the lower temperature requirements and because of the higher yields of extract product that can be obtained with liquid-phase operation over those obtained with vapor-phase operation.
Desorption conditions will thus include a temperature of about 20 to about ~00C and a pressure sufficient to maintain liquid-phase. Adsorptlon conditlons will include the same range of temperatures and pressures as used for desorption oonditions.
A static test procedure and apparatus may be employed to test various adsorbents with a partlcular feed m;xture to determine the relative retention by the adsorbent of each component of the m~xture. The procedure involves mixing together known quantities of each component, the relative retention of which is to be determined, and a convenient solvent or desorbent material. A desorbent is selected that will have a boiling point well separated from those of the ~ 2 ~ ~
isomers being tested. The resulting solution is then placed in a vessel with a quantity of the appropriate adsorbent and is allowed to remain, with occasional stirring, until equilibrium is attained. The solution is then analyzed for each component and the relative retention thereof is determined in terms of the ratio, R, of the more strongly adsorbed component to the less strongly adsorbed component.
Therefore, the lower the above ratio, the greater will be the relative retention of the more strongly adsorbed component by the adsorbent.
A dynamic testing apparatus is employed to test various adsorbents with a particular feed mixture and desorbent material to measure the adsorption characteristics of retention capacity and exchange rate. The apparatus consists of a helical adsorbent chamber of approximately 75 cc volume having inlet and outlet portions at opposite ends of the chamber. The chamber is contained within a temperature control means and, in addition, pressure control equipment is used to operate the chamber at a constant predetermined pressure. Quantitative and qualitative analytical equipment such as refractometers, polarirneters and chromatographs can be attached to the outlet line of the chamber and used to detect quantitatively or determine qualitatively one or more components in the effluent stream leaving the adsorbent chamber. A pulse test, performed using this apparatus and the following general procedure, is used to determine data for various adsorbent systems. The adsorbent is filled to equilibrium with a particular desorbent material by passing the desorbent material through the adsorbent chamber. At a convenient time, a pulse of feed containing known concentrations of a tracer and of a part;cular extract component or of a raffinate component or both, all diluted in desorbent material is injected for a duration of several minutes. Desorbent material flow is resumed, and the tracer and the extract component or the raffinate component (or both) are eluted as in a liquid-solid chromatographic operation. The effluent can beanalyzed on-stream or alternatively, effluent samples can be collected periodically and later analyzed separately by analytical equipment and traces of the envelopes or correspond;ng component peaks developed.
From information derived from the test, adsorbent performance can be rated in terms of void volume, retention volume for an extract or a raffinate component, and the rate of desorption of an extract component from the adsorbent.
The retention volume of an extract or a raffinate component may be characterized by the distance between the center of the peak envelope of an extract or raffinate component and the center of the peak envelope of the tracer component or some other known reference point. It ;s expressed in terms of the volume in cubic centimeters of desorbent material pumped during this time interval represented by the distance between the peak envelopes. The rate of exchange of an extract component with the desorbent material can generally be characterized by the width of the peak envelopes at half intensity. The narrower the peak width, the faster the desorption rate. The desorption rate can also be characterized by the distance between the center of the tracer peak envelope and the disappearance of an extract component which has just been desorbed. This distance is again the volume of desorbent material pumped during this time interval.
The following non-limiting examples are presented to illustrate the process of the present invention and are not intended to unduly restrict the scope of the claims attached hereto.
A number of static tests were performed as described hereinabove to demonstrate that it was possible to separate the isomers by an adsorptive process. A stock solution of toluenediamine (TDA) isomers as follows was used in the tests:
2,4-TDA 1.63 9 2,6-TDA 0.41 9 chloroform 50.0 cc In the static tests all at 25C, the volume ratio of stock solution to adsorbent was 3Ø The stock solution and adsorbent were combined in a flask and the amount of each isomer left in the raffinate was determined and the isomer ratio9 R = 2,4-TDA/2,6-TDA was calculated for a number of adsorbents. The results are as follows:
DSORBENT INITIAL 2,4/2,6 FINAL 2,4/2,6 Ni X 3.71 3.48 Ni Y 3.71 3.40 Ba X 3.71 2.78 BaK X 3.71 3.30 Ca X 3.71 3.32 Ca Y 3.71 2.98 K X 3.71 3.50 Na X 3.71 3.14 Selectivity is expressed by some change in the isomer ratio upon contact with a selective adsorbent. From the above table it is clear that selective adsorption of 2,4-TDA
was obtained in all cases. Hence that, in combination with an appropriate desorbent, these isomers may be separated by our adsorptive process. Several of these adsorbents also underwent the pulse test as described in the next example, confirming the results of the static test.
The previously described pulse test apparatus was used to obtain data for this example. The liquid temperature was 120C and the flow was up the column at the rate of 1.2 cc/min. The feed stream comprised 2.6 cc pulses of a solution containing 0.5 gm of 2,6-toluenediamine, 0.5 am of 2,4-toluenediamine and 0.12 gm of n-C14 tracer, all dissolved in 3 cc of desorbent. The column was packed with clay bound sodium-exchanged X zeolite adsorbent of 20-50 mesh particle size. The desorbent was 100~ ethanol.
The results of this example are shown in Figure 1. The adsorbent is 2,4-TDA-selective with a selectivity factor (B) of 1.66.
A number of other adsorbents showing 2,4-TDA
selectivity were tested in the same manner and the results set forth in the following Table 2 confirm the static test results:
Table 2 ADSOPBENT DESORBENT SELECTIVITY
(B 2,4-/2,6-) Ni-X 50/50 n-butyl amine/ 2.32 toluene Ni-X 90/10 methanol/H20* 4.53 Co-Y 30/20 methanol/H20* 3.16 Ca-Y lO0~ methanol 1.78 (Hydrated;
Ni-Y 70/30 methanol/H20* 3.39 *deionized water The pulse test apparatus was also used to obtain data for this example. The liquid temperature was 120C and the flow was up the column at the rate of 1.2 ml/min. The feed stream comprised 2.6 cc pulses of a solution containing 0.5 gm of 2,4~toluenediamine, 0.5 gm of 2,6-toluenediamine and 0.2 gm of p-diisopropylbenzene tracer9 all dissolved in 3 cc of desorbent. The solumn was pasked with clay bound barium-exchanged X zeolite adsorbent o~ 20~50 mesh particle size.
The desorbent was 100~ methanol.
The results of this example are shown in Figure 2. The adsorbent is 2,6-toluenediamine selective. The selectivity factor (B) 2,~-/2,4- is 6~59. In this case, the static test in Example 1 was not able to predict selectivity of the adsorbent under separation conditions involving an effective desorbent.
The pulse test apparatus was again used to obtain data for this example. The liquid temperature was 120C and the flow was up the column at the rate of 1.18 ml/min. The feed stream comprised 2.6 cc pulses of a solution containing 0.6 gm of commercial 80/20 2,4-TDA/2,6-TDA, 0.~ gm 2,6-TDA and 0.25 gm of mesitylene tracer, all dissolved in 3 gm of desorbent. The column was packed with clay bound potassium-exchanged L zeolite adsorbent of 20-50 mesh particle size.
The desorbent was 100~ methanol.
The results of this example are shown in Figure 3.
This adsorbent is also 2,6-toluenediamine selective; the selectivity factor (B) 2,6-/2,4- is 3.96. Separation by adsorption of the isomer in smaller amount is preferred in a commercial process since a greater quantity of feed can be processed per unit quantity of adsorbent and per unit of time.
Example 5 The adsorbent used in Example 4 was used to obtain pulse test data for this example. The feed stream comprised of a solution containing 0.3 gm of each of 2,4-TDA, 2,6-TDA,
BACKGROUND OF THE INVENTION
The isomers, 2,4-toluenediamine and 2,6-toluenediamine are important precursers of polyurethanes which are useful in many applications as rigid or flexible forms or as fibers, e.g., insulation, soundproofing, interlinings for clothing and sleeping bags, cushions, spandex, etc.
It is common industrial practice to make polyurethane from a mixture of the isomers, 2,4- and 2,6-toluene diisocyanate (TDI), for example 80/20 or 65/35, derived from mixtures of 2,4- and 2,6-toluenediamine, because it is difficult and expensive to separate them by existing techniques. Current methods of separating the isomers involve crystallization, e.g. U.S. Patent No. 4,246,187, and hence, are energy-intensive and time-consuming. Moreover, polyurethanes derived from pure 2,4-toluenediamine have dramatically different properties compared to materials synthesized from mixtures. It is further expected that polyurethanes synthesi~ed from (relatively3 pure 2,6-toluenediamine ~ill have different and more useful properties, for example, a higher glass transition temperature, Tg, a-nd greater stability. Also, the reaction speed with a single isomer is expected to be more consistent. Accordingly, it is desirable to separate the TDI isomers or their precursors, the toluenediamines, by an economical process.
It is well known in the separation art that certain crystalline aluminosilicates can be used to separate hydrocarbon types from mixtures thereof. Furthermore, X and Y zeolites have been employed in a number of processes to separate individual hydrocarbon isomers.
It is known from U.S. Patent No. 3,069,470 to Fleck et al, to use type X zeolites for the separation of the meta isomer from other isomers of toluidine. In U.S. Patent No.
4,4~0,129 to Priegnitz et al, it is disclosed to separate p-toluidine from its isomers with an X- or Y- type zeolite exchanged with Fe, Mn, Co, Ni or Zn and a desorbent comprising aniline or, when using an X-type zeolite, alkylamine having greater than eight carbons.
It is known from U.S. Patent No. 4,270,013 to Priegnitz et al that ortho-nitrotoluene may be separated From other nitrotoluene isomers by using a type X zeolite containing at exchangeable cationic sites one cation selected from a group that includes potassium and barium. The specific desorbent materials disclosed by this reference are toluene and 1-hexanol. The separation of isomers of disubstituted benzenes with crystalline aluminosilicates having silica/alumina mole ratio oF at least l2 is disclosed in U.S. Patent No. 4,~67,126 to Zinnen.
The adsorptive separation of another precursor of polyurethane, 2,4-dinitro toluene and 2,6-dinitrotoluene has been disclosed and the separation is achieved by an L, X or Y type zeolite cation exchanged with K, Na, Ca, Ba, Li or Mg and desorbed by a C3 to C5 alcohol, a ketone, ester or a nitrocompound.
The separation of minor isomers9 2,3- and 3~4-dinitrotoluene, from the major isomers, ~94- and ?,6-dinitrotoluene, with a calcium or sodium exchanged Y type zeolite hass been disclosed. The desorbent can be an ester, an alcohol or a ketone. Presence of the minor isomers lowers the yield of polyurethane precursors and produces high molecular weight side products.
Alternatively, the final precursor of polyurethane, toluene diisocyanate, is normally available as mixtures of isomers. It is known that the separation of 2,4- and 2,6-diisocyanate (TDI) can be performed by adsorption onto a type Y zeolite exchanged with K, Ca, Na, Li, H, and Mg and desorbed with toluene. It is hypothesized that polyurethanes made with a single, pure isomer of TnI may exhibit improved properties.
SUMMARY OF THE INVENTI_ In brief summary, the invention is, in one embodiment, a process for separating 2,4-toluenediamine from a mixture comprising 2,4-toluenediamine and at least one isomer thereof, such as 2,6-toluenediamine. The process comprises contacting ~he mixture at adsorption conditions with an adsorbent comprising an X type zeolite cation exchanged with a cation from the group Ca, Na, K, Ni or a Y- type zeolite exchanged with a cation from the group Ca or Ni cations, thereby selectively adsorbing the 2,4-toluenediamine thereon. The remainder of the feed mixture is then removed from the adsorbent and the 2,4-toluenediamine recovered by desorption at desorption conditions with a desorbent material comprising a lower alcohol or an amine. In the process using an X-type of zeolite cation, exchanged with a barium cation or an L-type zeolite exchanged with a K
cation, the zeolite is 2,6-toluenediamine selective and hence 2,6-toluenediamine will be adsorbed by the zeolite.
It is advantageous to use a 2,6-toluenediamine - selective zeolite with commercially available feed mixtures of toluenediamine isomers which are 80~ 2,4-toluenediamine and 20~ 2,6-toluenediamine because extraction of the minor 2,6-component results in a more efficient and economical separation. Effective desorbents for this separation , whether 2,4- selective or 2,6- selective, have been found to comprise lower alcohols, e.y. methanol and ethanol and n-alkyl amines.
Other embodiments of our invention encompass details about feed mixtures, adsorbents, desorbent materials and operating conditions, all of which are hereinafter disclosed in the following discussion of each of the facets of the present invention.
BRI~F DESCRIPTION OF THE DRAWING
Figures 1-5 are chromatographic traces representing the separation of the isomers of toluenediamine by the pulse test method using different zeolite adsorbents and desorbents as generated in Examples 2-6.
DESCRIPTION OF THE INVENTION
At the onset, the definitions of various terms used throughout the specification will be useful in making clear the operation, objects and advantages of our process.
A "feed mixture" is a mixture containing one or more e~tract components and one or more raffinate components to be separated by our process. The term "feed stream"
indicates a stream of a feed mixture which passes to the adsorbent used in the process.
An "extract component" is a compound or type of compound that is more selectively adsorbed by th~ adsorbent while a "raffinate component" is a compound or type of compound that is less selectively adsorbed. In this process, 2,4- toluenediamine is an extract component and 296- toluenediamine is a raffinate component, when the adsorbent used is Ca X, Na X, ~i X, K X, Ca Y or Ni Y.
However, when the adsorbent used is Ba X or K L, 2,h-toluenediamine is an extract component and 294-toluene-diamine is a raffinate component. The term "desorbent material" shall mean generally a material capable of desorbing an extract component. The term "desorbent stream"
or "desorbent input stream" indicates the stream through which desorbent material passes to the adsorbent. The term "raffinate stream" or "raffinate output stream" means a stream through which a raffinate component is removed from the adsorbent. The composition of the raffinate stream can vary from essentially 100~ desorbent material to essentially 100% raffinate components. The "extract stream" or "extract output stream" shall mean a stream through which an extract material which has been desorbed by a desorbent material is removed from the adsorbent. The composition of the extract stream, likewise, can vary from essentially 100% desorbent material to essentially 100% extract components. At least a portion of the extract stream and preferably at least a portion of the raffinate stream from the separation process are passed to separation means, typically fractionators, where at least a portion of the desorbent material is separated to produce an extract product and a raffinate product. The terms "extract product" and "raffinate product" mean products produced by the process containing, respectively, an extrac~ component and a raffinate component in higher concentrations than those found in the extract stream and the raffinate stream. Although it is possible by the process of this invention to produce a high purity product at high recoveries, it will be appreciated that an extract component is never completely adsorbed by the adsorbent, nor is a raffinate component completely nonadsorbed by the adsorbent. Therefore, varying amounts of a raffinate component can appear in the extract stream and, likewise, varying amounts of an extract component can appear in the raffinate stream. The extract and raffinate streams then are further distinguished from each other and from the feed mixture by the ratio of the concentrations of an extract component and a raffinate component appearing in the particular stream. More specifically, the ratio of the concentration of 2,4-toluenediamine (extract) to that of a less selectively adsorbed isomer, 2,6-toluenediamine (raffinate) will be lowest in the raffinate stream, next highest in the feed mixture, and the highest in the extract stream. Likewise, the ratio of the concentration of less selectively adsorbed 2,6-toluenediamine to that of more selectively adsorbed 2,~-toluenediamine will be highest in the raffinate stream, next highest in the feed mixture, and the lowest in the extract stream. In the embodiment where 2,6-toluenediamine is the selectively adsorbed compsnent~
the above ratios are reversed.
The term "selective pore volume" of the adsorbent is defined as the volume of the adsorbent which se1ectively adsorbs an extract component from the feed mixture. The term "non-selective void volume" of the adsorbent is the volume of the adsorbent which does not selectively retain an extract component from the feed mixture. This volume includes the cavities of the adsorbent which contain no adsorptive sites and the interstitial void spaces between adsorbent particles. The selective pore volume and non~
selective void volume are generally expressed in volumetric quantities and are of importance in determining the proper flow rates of fluid required to be passed into an operational zone for efficient operations to take place for a given quantity of adsorbent. When adsorbent "passes" into the operational zone employed in one embodiment of this process, its non-selective void volume together with its selective pore volume carries fluid into that zone. The non-selective void volume is utilized in determining the amount of fluid which should pass into the same zone in a countercurrent direction to the adsorbent to displace the fluid present in the non-selective void volume. If the fluid flow rate passing into a zone is smaller than the non-selective void volume rate of adsorbent material passing into that zone~ there is a net entrainment of liquid into the zone by the adsorbent. Since this net entrainment is a fluid present in the non-selective void volume of the ~ 3~ ~
adsorbent, it in most instances comprises less selectively retained feed components. The selective pore volume of an adsorbent can in certain instances adsorb portions of raffinate material from the fluid surrounding the adsorbent since in certain instances there is competition between extract material and raffinate material for adsorptive sites within the selective pore volume. If a large quantity of raffinate material with respect to extract material surrounds the adsorbent, raffinate material can be competitive enough to be adsorbed by the adsorbent.
The prior art has recognized that certain characteristics of adsorbents are highly desirable, if not absolutely necessary, to the successful operation of a selective adsorption process. Such characteristics are equally important to this process. Among such characteristics are: adsorptive capacity for some volume of an extract component per volume of adsorbent, the selective adsorption of an extract component with respect to a raffinate component and the desorbent material; and sufficiently fast rates of adsorption and desorption of an extract component to and from the adsorbent. Capacity of the adsorbent for adsorbing a specific volume of an extract component is, of course, a necessity; without such capacity the adsorbent is useless for adsorptive separation.
Furthermore, the higher the adsorbent's capacity for an extract component the better is the adsorbent. Increased capacity of a particular adsorbent makes it possible to reduce the amount of adsorbent needed to separate an extract component of known concentration contained in a particular charge rate of feed mixture. A reduction in the amount of adsorbent required for a specific adsorptive separation reduces the cost of a separation process. It is important that the good initial capacity of the adsorbent be maintained during actual use in the separation process over some economically desirable life.
The second necessary adsorbent characteristic is the ability of the adsorbent to separate components of the ~eed;
or, in other words, that the adsorbent possess adsorptive se1ectivity for one component as compared to another component. Relative selectivity can be expressed not only for one ~eed component as compared to another but can also be expressed between any feed mixture component and the desorbent material. The selectivity, (B), is defined as the ratio of the two components of the adsorbed phase divided by the ratio of the same two components in the unadsorbed phase at equilibrium condition, as shown in Equation 19 below:
Selectivity = (B) = ~vol. percent C/vol. percent D~A
~vol. percent C/vol. percent D~U
where C and D are two components of the feed represented in volume percent and the subscripts A and U represent the adsorbed and unadsorbed phases respectively. The equilibrium conditions were determined when the feed passing over a bed of adsorbent did not change composition after contacting the bed of adsorbent. In other words, there was no net transfer of material occurring between the unadsorbed and adsorbed phases. Where selectivity of two components approaches 1.0, there is no preferential adsorption of one component by the adsorbent with respect to the other; they are both adsorbed (or non-adsorbed) to about the same degree with respect to each other. As the (B) becomes less than or greater than 1.0, there is a pre~erential adsorption by the adsorbent for one component with respect to the other. When comparing the selectivity by the adsorbent of one component C over component D, a (B) larger than 1.0 indicates preferential adsorption of component C within the adsorbent.
A (B) less than 1.0 would indicate that component D is preferentially adsorbed leaving an unadsorbed phase richer in component C and an adsorbed phase richer in component D.
~ ~ 2 3~ ~
The third important characteristic is the rate of exchange of the extract component of the feed mixture material or, in other words, the relative rate of desorption of khe extract component. This characteristic relates directly to the amount of desorbent material that must be employed in the process to recover the extract component from the adsorbent, faster rates of exchange reduce the amount of desorbent mat~rial needed to remove the extract component and therefore permit a reduction in the operating cost of the process. With faster rates of exchange, less desorbent material has to be pumped through thP process and separated from the extract stream for reuse in the process.
Adsorbents to be used in the process of this invention will comprise specific crystalline aluminosilicates.
Particular crystalline aluminosilicates encompassed by the present invention include crystalline aluminosilicate cage structures in which the alumina and silica tetrahedra are intimately connected in an open three dimensional network to form cage-like structures with window-like pores of about 8 A free diameter. The tetrahedra are crosslinked by the sharing of oxygen atoms with spaces between the tetrahedra occupied by water molecules prior to partial or total dehydration of this zeolite. The dehydration of the zeolite results in crystals interlaced with cells having molecular dimensions and thus the crystalline aluminosilicates are often referred to as "molecular sieves", particuarly when the separation which they effect is dependent essentially upon differences between the sizes of the feed molecules as, for instance, when smaller normal paraffin molecules are separated from larger isoparaffin molecules by using a particular molecular sieve.
In hydrated form, the crystalline aluminosilicates used in the process of this invention generally encompass those zeolites represented by the Formula 1 below:
~ ~ 23 Formula I
M2/no:Al2o3:wsio2 y~2o where "M" is a cation which balances the electrovalence of the aluminum-centered tetranedra and wh;ch is generally referred to 35 an exchangeable cationic site, "n" represents the valence of the cation, "w" represents the moles of SiO2, and "y" represents the moles of water. The generalized cation "M" may be monovalent, divalent or trivalent or mixtures thereof.
The prior art has generally recogn;zed that adsorbents comprising L, X and Y zeolites can be used in certain adsorptive separation processes. These zeolites are described and defined in U.S. Patent Nos. 3,216,789, 2,882,244 and 3,130,007, respectively.
The X zeolite in the hydrated or partially hydrated form can be represented in terms of mole oxides as shown in Formula 2 below:
Formu1a 2 (o.9~o.2)M2~no:Al2o3:(2.5+o.5)sio2 yH2o where "M" represents at least one cation having a valence of not more than 3, "n" represents the valence of "M" and "y"
is a value up to about 9 depending upon the identity of "M"
and the degree of hydration of the crystal. As noted from Formula 29 the SiO2/A1203 mole ratio of X zeolite ls 2.5+0.5. The cation "M" may be one or more of a number of cations such as a hydrogen cation, an alkal~ metal catlon, or an alkaline earth cation, or other selected cations~ and is generally referred to as an exchangeable cationic site.
As the X zeollte is initially prepared, the cation "M" is usually predomlnately sodium, that ls, the major cation at the exchangeable cationic sites is sodium and the zeolite is therefore referred to as a sodium-X zeolite. Depending upon ~:'."', the purity of the reactants used to make the zeolite, other cations mentioned above may be present, however, as impurities. The Y zeolite in the hydrated or partially hydrated form can be similarly represented in the terms of mole oxides as in Formula 3 below:
Formula 3 (o~9+o~2)M2/no:Al2o3:wsio2 yH2o where "M" is at least one cation having a valence not more than 3, "n" represents the valance of "M", "w" is a value greater than about 3 up to about 6, and "y" is a value up to about 9 depending upon the identity of "M" and the degree of hydration of the crystal. The SiO2/Al203 mole ratio for Y
zeolites can thus be from about 3 to about 6. Like the X
zeolite, the cation "M" may be one or more of a variety of cations but, as the Y zeolite is initially prepared, the cation "M" is also usually predominately sodium. A Y
zeolite containing predominately sodium cations at the exchangeable cationic sites is therefore referred to as a sodium-Y zeolite or Na-Y zeolite.
The L zeolite in the hydrated or partially hydrated form may be represented in terms of mole oxides as in Formula 4 below:
Formula 4 o.g 1.3M2/no:Al2o3:5-2-6 9SiO2 y 2 where M designates at least one exchangeable cation as referred to above, n is the valence of M and y may be any value from O to about 9. It is preferred to synthesize the potassium form of the L-type zeolite since the reactants to make this form are readily available and generally water soluble. Thus the as-made form of the L-zeolite is referred to as potassium-L, or K-L, zeolite. L-zeolite is characterized by planar 12-ring pores aligned to produce ~ 3~ ~
one-dimensional channels, linked to each other by small pore openings which will not admit water molecules. A minor two-dimensional pore system also exists, parallel to the aforesaid channels.
Cations occupying exchangeable cationic sites in the zeolite may be replaced with other cations by ion exchange methods well-known to those having ordinary skill in the field of crystalline aluminosilicates. Such methods are generally performed by contacting the zeolite or an adsorbent mater~al containing the zeolite with an aqueous solution of the soluble salt of the cation or cations desired to be placed upon the zeolite. After the desired degree of exchange takes place, the sieves are removed from the aqueous solution, washed, and dried to a desired water content. By such methods the sodium cations and any non-sodium cations which might be occupying exchangeable sites as impurities in a sodium-X or sodium-Y zeolite can be par~ially or essentially completely replaced with other cations. The zeolite used in the process of this invention contains cations at exchangeable cationic sites selected from the group of metals K, Na, Ca, Ba,Co or Ni. The preferred zeolites are Ba X and K L~ which are selective for the minor isomer, 2,6-toluenediamine.
Typically, adsorbents used in separative processes contain zeolite crystals dispersed in an amorphous material or inorganic matrix. The zeolite will typically be present in the adsorbent in amounts ranging from about 75 to about 98 wt. % based on volatile-free composition. Volatile-free compositions are generally determined after the adsorbent has been calcined at 900C in order to drive off all volatile matter. The remainder of the adsorbent will generally be the inorganic matrix material such as silica, titania, or alumina or mixtures thereof, or compounds, such as clays, which material is present in intimate mixture with the small particles of the zeolite material. This matrix material may be an adjunct of the manufacturing process for ~ 3~ ~
zeolite (for example, intentionally 1ncomplete purification of elther zeolite during its manu~acture) or it may be added to relatively pure zeolite, but ln either case its usual purpose is as a binder to aid in forming or agglomerating the hard crystalline particles of the zeolite. Normally, the adsorbent will be in the form of particles such as extrudates, aggregates9 tablets, macrospheres or granules having a desired particle size range. The typical adsorbent will have a particle size range of about 16-6~ mesh (Standard U.S. Mesh). Examples of zeolites used in adsorbents known to the art, e~ther as is or after cation exchange, are "Molecular S;eves 13Xi' and SK-40" both of which are available from the Linde Company, Tonawanda, New York. The first material contains X zeolite wh;le the latter material contains Y zeolite.
Ideally, desorbent materials should have a selectivity equal to about 1 or slightly less than 1 with respect to all extract components so that all of the extract components can be desorbed as a class with reasonable flow rates of desorbent material and so that extract components can displace desorbent material in a subsequent adsorption step.
While separation of an extract component from a raf~lnate component is theoretically possible when the selectivity oF
the adsorbent for the extract component with respect to the raffinate component is ~ust slightly greater than 1.09 it is preferred that such selectivity be reasonably greater than 1Ø Like relative volatility, the hiyher the selectivity, the easier the separation is to perform. Higher selectivities permit a smaller amount of adsorbent to be used.
Desorbent materials used in various prior art adsorptive separation processes vary depending upon such factors as the type of operation employed. In the swing bed system in which the selectively adsorbed feed component is removed from the adsorbent by a purge stream desorbent~
selection is not as cr;tical and desorbent materials * Trade Mark ,~ ~
comprising gaseous hydrocarbons such as methane, ethane, etc., or other types of gases such as nitrogen or hydrogen may be used at elevated temperatures or reduced pressures or both to effectively purge the adsorbed feed component from the adsorbent. However, in adsorptive separation processes which are generally operated continuously at substantially constant pressures and temperatures to insure liquid phase, the desorbent material must be judiciously selected to satisfy many criteria. First, the desorbent material should displace an extract component from the adsorbent with reasonable mass flow rates without itself being so strongly adsorbed as to unduly prevent an extract component from displacing the desorbent material in a following adsorption cycle. Expressed in terms of the selectivity (hereafter discussed in more detail)9 it is preferred that the adsorbent be more selective for all of the extract components with respect to a raffinate component than it is for the desorbent material with respect to a raffinate component. Secondly, desorbent materials must be compatible with the particular adsorbent and the particular feed mixture. More specifically, they must not reduce or destroy the critical selectivity of the adsorbent for an extract component with respect to a raffinate component. Desorbent materials should additionally be substances which are easily separable from the feed mixture that is passed into the process. Both the raffinate stream and the extract stream are removed fro~ the adsorbent in admixture with desorbent material and without a method of separating at least a portion of the desorbent material, the purity of the extract product and the raffinate product would not be very high nor would the desorbent material be available for reuse in the process. It is therefore contemplated that any desorbent material used in this process will preferably have a substantially different average boiling point than that of the feed mixture to allow separa~ion of at least a portion of desorbent material from feed components in the extract and raffinate streams by simple fractional distillation, thereby permitting reuse of desorbent material in the process. The term "substantially different" as used herein shall mean that the difference between the average boiling points between the desorbent material and the feed mixture shall be at least about 5C. The boiling range of the desorbent material may be higher or lower than that of the feed mixture. Finally, desorbent materials should also be materials which are readily available and therefore reasonable in cost. In the preferred isothermal, isobaric, liquid-phase operation of the process of our invention, we have found that desorbent material comprising a lower alcohol, e.g. 9 methanol, ethanol, propanol or amines, e.g.
n-alkylamines, etc. will result in selectivity for the 2,4-toluenediamine isomer when used with an adsorbent selected from the group comprising Ca X, Na X, K X, Ni X, Ca Y or Ni Y and will result in selectivity for the 2,6- isomer when the absorbent is selected from the group Ba X or K L.
Methanol is the most preferred desorbent in this process.
Toluene, which acts as a diluent for the desorbent, can be used with any desorbent in amounts up to about 50 vol.%.
Certain combinations of adsorbent and desorbent were found to be most effective in separating the TDA isomers and therefore 9 the most preferred adsorbent-desorbent combinations are K-L zeolite with methanol desorbent, Na X
zeolite with ethanol and Ba X zenlite with methanol desorbent. Each of these combinations exhibited, in the pulse tests, good selectivity and resolution and well-shaped elution profiles. Furthermore, these desorbents are inexpensive, available chemicals, having low boiling points with respect to the TDA isomers.
The adsorbent may be employed in the form of a dense compact fixed bed which is alternatively contacted with the feed mixture and desorbent materials. In the simplest embodiment of the invention, ~he ~dsorbent is employed in the form of a single static bed in which case the process is only semi-continuous. In another embodiment, a set of two or more static beds may be employed in fixed bed contacting with appropriate valving so that the feed mixture is passed through one or more adsorbent beds while the desorbent materials can be passed through one or more of the other beds in the set. The flow of feed mixture and desorbent materials may be either up or down through the desorbent.
Any of the conventional apparatus employed in static bed fluid-solid contacting may be used.
Moving bed or simulated moving bed flow systems, however, have a much greater separat~on efficiency than fixed bed systems and are therefore preferred. In the moving bed or simulated moving bed processes 9 the retention and displacement operations are continuously taking place wh;ch allows both continuous production of an extract and a raffinate stream and the continuous use of feed and displacement fluid streams. One preferred embodiment of this process utilizes what is known in the art as the simulated moving bed countercurrent flow system. The operating principles and sequence of such a flow system are described in U.S. Patent No. 2,985,589.
In such a system, it is the progressive movement of multiple liquid access points down a molecular sieve chamber that simulates the upward movement of molecular sieve contained in the chamber. Reference can also be made to D.B. Broughton's U.S. Patent No. 2,985,589 and to a paper entitled, "Continuous Adsorptive Processing -A New Separation Technique" by D.B. Broughton presented at the 34th Annual Meeting of the Society of Chemical Engineers at Tokyo, Japan on April 2, 1969, for further explanation of the simulated moving bed countercurrent process flow scheme.
Another embodiment of a simulated moving bed flow system suitable for use in the process of the present invention is the co-current high efficiency simulated moving ~ .
~ 3~ ~
bed process disclosed in our assignee's U.S. Patent No.
4,402,~32.
It is contemplated with any flow scheme used to carry out the present invention that at least a portion of the extract output stream will pass into a separation means wherein at least a portion of the desorbent material can be separated to produce an extract product containing a reduced concentration of desorbent material. Preferably, but not necessary to the operatlon of the process, at least a portion of the raffinate output stream will also be passed to a separation means wherein at least a portion of the des~rbent material can be separated to produce a desorbent material stream which can be reused in the process and a raffinate product containing a reduced concentration of desorbent material. The separation means will typically be a fractionation column, the design and operation of wh~ch is well-known to the separation art.
Although both liquid and vapor phase operations can be used in many adsorptive separation processes, liquid-phase operat10n is preferred for this process because of the lower temperature requirements and because of the higher yields of extract product that can be obtained with liquid-phase operation over those obtained with vapor-phase operation.
Desorption conditions will thus include a temperature of about 20 to about ~00C and a pressure sufficient to maintain liquid-phase. Adsorptlon conditlons will include the same range of temperatures and pressures as used for desorption oonditions.
A static test procedure and apparatus may be employed to test various adsorbents with a partlcular feed m;xture to determine the relative retention by the adsorbent of each component of the m~xture. The procedure involves mixing together known quantities of each component, the relative retention of which is to be determined, and a convenient solvent or desorbent material. A desorbent is selected that will have a boiling point well separated from those of the ~ 2 ~ ~
isomers being tested. The resulting solution is then placed in a vessel with a quantity of the appropriate adsorbent and is allowed to remain, with occasional stirring, until equilibrium is attained. The solution is then analyzed for each component and the relative retention thereof is determined in terms of the ratio, R, of the more strongly adsorbed component to the less strongly adsorbed component.
Therefore, the lower the above ratio, the greater will be the relative retention of the more strongly adsorbed component by the adsorbent.
A dynamic testing apparatus is employed to test various adsorbents with a particular feed mixture and desorbent material to measure the adsorption characteristics of retention capacity and exchange rate. The apparatus consists of a helical adsorbent chamber of approximately 75 cc volume having inlet and outlet portions at opposite ends of the chamber. The chamber is contained within a temperature control means and, in addition, pressure control equipment is used to operate the chamber at a constant predetermined pressure. Quantitative and qualitative analytical equipment such as refractometers, polarirneters and chromatographs can be attached to the outlet line of the chamber and used to detect quantitatively or determine qualitatively one or more components in the effluent stream leaving the adsorbent chamber. A pulse test, performed using this apparatus and the following general procedure, is used to determine data for various adsorbent systems. The adsorbent is filled to equilibrium with a particular desorbent material by passing the desorbent material through the adsorbent chamber. At a convenient time, a pulse of feed containing known concentrations of a tracer and of a part;cular extract component or of a raffinate component or both, all diluted in desorbent material is injected for a duration of several minutes. Desorbent material flow is resumed, and the tracer and the extract component or the raffinate component (or both) are eluted as in a liquid-solid chromatographic operation. The effluent can beanalyzed on-stream or alternatively, effluent samples can be collected periodically and later analyzed separately by analytical equipment and traces of the envelopes or correspond;ng component peaks developed.
From information derived from the test, adsorbent performance can be rated in terms of void volume, retention volume for an extract or a raffinate component, and the rate of desorption of an extract component from the adsorbent.
The retention volume of an extract or a raffinate component may be characterized by the distance between the center of the peak envelope of an extract or raffinate component and the center of the peak envelope of the tracer component or some other known reference point. It ;s expressed in terms of the volume in cubic centimeters of desorbent material pumped during this time interval represented by the distance between the peak envelopes. The rate of exchange of an extract component with the desorbent material can generally be characterized by the width of the peak envelopes at half intensity. The narrower the peak width, the faster the desorption rate. The desorption rate can also be characterized by the distance between the center of the tracer peak envelope and the disappearance of an extract component which has just been desorbed. This distance is again the volume of desorbent material pumped during this time interval.
The following non-limiting examples are presented to illustrate the process of the present invention and are not intended to unduly restrict the scope of the claims attached hereto.
A number of static tests were performed as described hereinabove to demonstrate that it was possible to separate the isomers by an adsorptive process. A stock solution of toluenediamine (TDA) isomers as follows was used in the tests:
2,4-TDA 1.63 9 2,6-TDA 0.41 9 chloroform 50.0 cc In the static tests all at 25C, the volume ratio of stock solution to adsorbent was 3Ø The stock solution and adsorbent were combined in a flask and the amount of each isomer left in the raffinate was determined and the isomer ratio9 R = 2,4-TDA/2,6-TDA was calculated for a number of adsorbents. The results are as follows:
DSORBENT INITIAL 2,4/2,6 FINAL 2,4/2,6 Ni X 3.71 3.48 Ni Y 3.71 3.40 Ba X 3.71 2.78 BaK X 3.71 3.30 Ca X 3.71 3.32 Ca Y 3.71 2.98 K X 3.71 3.50 Na X 3.71 3.14 Selectivity is expressed by some change in the isomer ratio upon contact with a selective adsorbent. From the above table it is clear that selective adsorption of 2,4-TDA
was obtained in all cases. Hence that, in combination with an appropriate desorbent, these isomers may be separated by our adsorptive process. Several of these adsorbents also underwent the pulse test as described in the next example, confirming the results of the static test.
The previously described pulse test apparatus was used to obtain data for this example. The liquid temperature was 120C and the flow was up the column at the rate of 1.2 cc/min. The feed stream comprised 2.6 cc pulses of a solution containing 0.5 gm of 2,6-toluenediamine, 0.5 am of 2,4-toluenediamine and 0.12 gm of n-C14 tracer, all dissolved in 3 cc of desorbent. The column was packed with clay bound sodium-exchanged X zeolite adsorbent of 20-50 mesh particle size. The desorbent was 100~ ethanol.
The results of this example are shown in Figure 1. The adsorbent is 2,4-TDA-selective with a selectivity factor (B) of 1.66.
A number of other adsorbents showing 2,4-TDA
selectivity were tested in the same manner and the results set forth in the following Table 2 confirm the static test results:
Table 2 ADSOPBENT DESORBENT SELECTIVITY
(B 2,4-/2,6-) Ni-X 50/50 n-butyl amine/ 2.32 toluene Ni-X 90/10 methanol/H20* 4.53 Co-Y 30/20 methanol/H20* 3.16 Ca-Y lO0~ methanol 1.78 (Hydrated;
Ni-Y 70/30 methanol/H20* 3.39 *deionized water The pulse test apparatus was also used to obtain data for this example. The liquid temperature was 120C and the flow was up the column at the rate of 1.2 ml/min. The feed stream comprised 2.6 cc pulses of a solution containing 0.5 gm of 2,4~toluenediamine, 0.5 gm of 2,6-toluenediamine and 0.2 gm of p-diisopropylbenzene tracer9 all dissolved in 3 cc of desorbent. The solumn was pasked with clay bound barium-exchanged X zeolite adsorbent o~ 20~50 mesh particle size.
The desorbent was 100~ methanol.
The results of this example are shown in Figure 2. The adsorbent is 2,6-toluenediamine selective. The selectivity factor (B) 2,~-/2,4- is 6~59. In this case, the static test in Example 1 was not able to predict selectivity of the adsorbent under separation conditions involving an effective desorbent.
The pulse test apparatus was again used to obtain data for this example. The liquid temperature was 120C and the flow was up the column at the rate of 1.18 ml/min. The feed stream comprised 2.6 cc pulses of a solution containing 0.6 gm of commercial 80/20 2,4-TDA/2,6-TDA, 0.~ gm 2,6-TDA and 0.25 gm of mesitylene tracer, all dissolved in 3 gm of desorbent. The column was packed with clay bound potassium-exchanged L zeolite adsorbent of 20-50 mesh particle size.
The desorbent was 100~ methanol.
The results of this example are shown in Figure 3.
This adsorbent is also 2,6-toluenediamine selective; the selectivity factor (B) 2,6-/2,4- is 3.96. Separation by adsorption of the isomer in smaller amount is preferred in a commercial process since a greater quantity of feed can be processed per unit quantity of adsorbent and per unit of time.
Example 5 The adsorbent used in Example 4 was used to obtain pulse test data for this example. The feed stream comprised of a solution containing 0.3 gm of each of 2,4-TDA, 2,6-TDA,
3,4-TDA and 1,3.5-triethyl benzene tracer, all dissolved in 3 gm of desorbent, to determine the effect of other TDA
isomers on the separation. The desorbent was 100% methanol.
As seen in Figure 4 this adsorbent is still 2,6-TDA
selective and the normally minor isomer, 3,4-TDA is eluted before 2,4-TDA.
Example 6 The adsorbent used in Example 3 was used to obtain pulse test data for this example in which the feed includes another isomer which can be found in minor components as impurities commercially available TDA feed materials. The flow rate was 1.08 ml/min. The feed stream comprised a solution containing 0.3 gm each of 2,6-TDA, 2~4-TDA and 3,4-TDA and 0.2 gm of triethylbenzene tracer, all dissolved in 3 gm of desorbent. The desorbent was 100% methanol, as in Example 3.
The adsorbent still exhibits 2.6-selectivity and the 3,4- isomer is eluted substantially with the 234- isomer, as seen in Figure 5.
isomers on the separation. The desorbent was 100% methanol.
As seen in Figure 4 this adsorbent is still 2,6-TDA
selective and the normally minor isomer, 3,4-TDA is eluted before 2,4-TDA.
Example 6 The adsorbent used in Example 3 was used to obtain pulse test data for this example in which the feed includes another isomer which can be found in minor components as impurities commercially available TDA feed materials. The flow rate was 1.08 ml/min. The feed stream comprised a solution containing 0.3 gm each of 2,6-TDA, 2~4-TDA and 3,4-TDA and 0.2 gm of triethylbenzene tracer, all dissolved in 3 gm of desorbent. The desorbent was 100% methanol, as in Example 3.
The adsorbent still exhibits 2.6-selectivity and the 3,4- isomer is eluted substantially with the 234- isomer, as seen in Figure 5.
Claims (10)
1. A process for separating a feed mixture comprising 2,4 toluenediamine and 2,6-toluenediamine, said process comprising contacting said mixture at adsorption conditions with an adsorbent comprising an X type zeolite, cation exchanged with a cation selected from the group Ni, Ca, Ba, K and Na, or a Y type zeolite exchanged with a cation selected from the group Ca and Ni cations or an L type zeolite exchanged with a K cation, thereby selectively adsorbing one of said toluene diamine isomers, removing the remainder of said mixture from said adsorbent, and then recovering said adsorbed toluene diamine isomer by contacting the adsorbent at desorption conditions with a desorbent material comprising a lower alcohol or an amine.
2. The process of Claim 1 wherein said adsorption and desorption conditions include a temperature within the range of from about 20°C to about 200°C and a pressure sufficient to maintain liquid phase.
3. The process of Claim 1 wherein said process is effected with a simulated moving bed flow system.
4. The process of Claim 1 wherein said process is effected with a static bed system.
5. The process of Claim 1 wherein said desorbent comprises a lower alcohol.
6. The process of Claim 1 wherein said desorbent comprises an alkyl amine.
7. The process of Claim 6 wherein said desorbent additionally contains toluene.
8. The process of Claim 1 wherein said desorbent is selected from the group consisting of n- butyl amine, methanol and ethanol.
9. The process of Claim 8 wherein said desorbent additionally contains ethanol.
10. The process of Claim 1 wherein said adsorbent is a Ba-exchanged X zeolite or a K-exchanged L zeolite and said selectively adsorbed toluenediamine isomer is 2,6-toluenediamine.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/811,623 US4633018A (en) | 1985-12-20 | 1985-12-20 | Process for separating isomers of toluenediamine |
| US811,623 | 1985-12-20 |
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| Publication Number | Publication Date |
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| CA1262360A true CA1262360A (en) | 1989-10-17 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000525887A Expired CA1262360A (en) | 1985-12-20 | 1986-12-19 | Process for separating isomers of toluenediamine |
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| Country | Link |
|---|---|
| US (1) | US4633018A (en) |
| EP (1) | EP0231496B1 (en) |
| JP (1) | JPS6310747A (en) |
| KR (1) | KR900000868B1 (en) |
| CN (1) | CN1008814B (en) |
| AR (1) | AR242774A1 (en) |
| AU (1) | AU590038B2 (en) |
| BR (1) | BR8606382A (en) |
| CA (1) | CA1262360A (en) |
| DE (1) | DE3672247D1 (en) |
| ES (1) | ES2015872B3 (en) |
| IN (2) | IN166969B (en) |
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| US20160159734A1 (en) * | 2013-08-19 | 2016-06-09 | Covestro Deutschland Ag | Process for obtaining organic isocyanates from distillation residues from isocyanate preparation |
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| DE3724018A1 (en) * | 1987-07-21 | 1989-02-02 | Bayer Ag | METHOD FOR SEPARATING ANILINE DERIVATIVES |
| EP0320879A1 (en) * | 1987-12-14 | 1989-06-21 | Air Products And Chemicals, Inc. | Separating toluenediamine from N-tertiarybutyl toluenediamine |
| US4996322A (en) * | 1989-05-15 | 1991-02-26 | Air Products And Chemicals, Inc. | Separation of amides with molecular sieves |
| US5174979A (en) * | 1989-10-06 | 1992-12-29 | Uop | Mixed ion-exchanged zeolites and processes for the use thereof in gas separations |
| FR2789914B1 (en) | 1999-02-22 | 2001-04-06 | Ceca Sa | SINTERED BINDER ZEOLITIC ADSORBENTS WITH LOW INERT BINDER, PROCESS FOR OBTAINING SAME AND USES THEREOF |
| US6469212B1 (en) | 2000-03-20 | 2002-10-22 | Albemarle Corporation | Separation of 2,4-toluenediamine from an isomeric mixture of toluenediamines |
| US6359177B1 (en) * | 2000-12-15 | 2002-03-19 | Bayer Corporation | Process for separating mixtures of materials having different boiling points |
| CN101875614A (en) * | 2009-12-10 | 2010-11-03 | 甘肃银达化工有限公司 | Method for recovering m-diaminotoluene from dinitrotoluene hydrogenated tar |
| DE102017207817A1 (en) * | 2017-05-09 | 2018-11-15 | Clariant International Ltd | Zeolite-containing adsorbent for the selective separation of isomers from aromatic hydrocarbon mixtures, its preparation and use |
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| US3069470A (en) * | 1958-07-21 | 1962-12-18 | Union Oil Co | Separation of toluidine isomers |
| US4371721A (en) * | 1978-12-14 | 1983-02-01 | Mobil Oil Corporation | Selective cracking of disubstituted benzenes having polar substituents |
| US4246187A (en) * | 1979-07-17 | 1981-01-20 | E. I. Du Pont De Nemours And Company | Separation of 2,4-tolylene diisocyanate from mixtures of 2,4- and 2,6-tolylene diisocyanate |
| US4270013A (en) * | 1979-10-19 | 1981-05-26 | Uop Inc. | Process for the separation of nitrotoluene isomers |
| DE3213876A1 (en) * | 1982-04-15 | 1983-11-17 | Hoechst Ag, 6230 Frankfurt | METHOD FOR PRODUCING O-TOLUIDIN AND / OR M-TOLUIDIN AND / OR P-TOLUIDIN |
| US4467126A (en) * | 1983-07-18 | 1984-08-21 | Uop Inc. | Process for the separation of di-substituted benzene |
| US4480129A (en) * | 1983-09-29 | 1984-10-30 | Uop Inc. | Process for separating isomers of toluidine |
-
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- 1985-12-20 US US06/811,623 patent/US4633018A/en not_active Expired - Fee Related
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|---|---|---|---|---|
| US20160159734A1 (en) * | 2013-08-19 | 2016-06-09 | Covestro Deutschland Ag | Process for obtaining organic isocyanates from distillation residues from isocyanate preparation |
| US9688619B2 (en) * | 2013-08-19 | 2017-06-27 | Covestro Deutschland Ag | Process for obtaining organic isocyanates from distillation residues from isocyanate preparation |
Also Published As
| Publication number | Publication date |
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| IN166969B (en) | 1990-08-11 |
| ES2015872B3 (en) | 1990-09-16 |
| CN1008814B (en) | 1990-07-18 |
| DE3672247D1 (en) | 1990-08-02 |
| KR900000868B1 (en) | 1990-02-17 |
| JPS6310747A (en) | 1988-01-18 |
| EP0231496B1 (en) | 1990-06-27 |
| AU6676786A (en) | 1987-06-25 |
| AR242774A1 (en) | 1993-05-31 |
| EP0231496A1 (en) | 1987-08-12 |
| BR8606382A (en) | 1987-10-13 |
| IN167120B (en) | 1990-09-01 |
| KR870005962A (en) | 1987-07-08 |
| US4633018A (en) | 1986-12-30 |
| CN86108766A (en) | 1987-08-05 |
| AU590038B2 (en) | 1989-10-26 |
| ZA869511B (en) | 1987-08-26 |
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